Applying parametric optimisation in the concept exploration phase on naval support vessels

Abstract

Five naval support vessels are being replaced. For this replacement two focus points are important. The first one concerns creating more unity within the fleet, achieved by using the hull geometry as a monolithic part. The second one concerns the aim to reduce harmful emissions by reducing the effects of the energy transition by minimising the resistance of the vessels. The current design approach at DMO has deficiencies which limit the ability to vary hull forms and to analyse a large set of design options. Also propulsion power is predicted by regression lines only, which makes it difficult to evaluate novel hull forms. Motion predictions are only used in a later design phase. These deficiencies need to be resolved. The technological opportunities which will be used to address these deficiencies are incorporating CAESES and RAPID in the concept exploration phase. CAESES is a CAD method with integrated optimisation algorithms which makes it useful to make hull form variations by using parametric optimisation. RAPID is a potential flow solver which can be used to predict the wave resistance on the geometry. The total resistance will be predicted by using Holtrop and Mennen for the viscous resistance components. The seakeeping capabilities are predicted by a simplified version of the linear strip theory. The main objective can be formulated as: How can the unity and the energy transition be analysed in the concept exploration phase for the new generation naval support vessels with a hull geometry point of view using RAPID/Holtrop/seakeeping integrated with CAESES Four validation studies have been performed. The test case studies are analysed on the differences in effective power and vertical displacement. The first conclusion is that the effective power will increase for a family design strategy in comparison to a single ship design strategy. The second conclusion is that the vertical displacement can be decreased when using a family design in comparison to the single design strategy. But only when the Logistic Support vessel is left out of the family of vessels, because of its restricted length. The design speed can be used as a design variable, but only when a more sophisticated power usage objective is used. The new approach can be very useful in the concept exploration phase at DMO. The new approach uses a more advanced resistance objective in combination with hull variation. It can also predict the seakeeping capabilities in the concept exploration phase already. The integration of a potential flow solver and prediction on vertical displacement at the bow can be done within one optimisation and a study is possible within reasonable time (under six hours). This makes the new approach practical in the concept exploration phase.